Hemostatic factors in rabbit limb lymph: relationship to mechanisms regulating extravascular coagulation

Mechanisms regulating extravascular coagulation in interstitial fluids of peripheral tissues are poorly understood, since measurements of hemostatic factors in these fluids are unavailable. Because lymph from a body region reflects the composition of its interstitial fluid, we measured hemostatic factors in limb lymph of rabbits both as activity and as antigen. Mean lymph-to-plasma activity ratios were the following: fibrinogen, 0.28; prothrombin, 0.26; factor X, 0.27; factor VII, 0.17; and factors V and VIII, 0.08. All lymph fibrinogen was clottable; fibrin degradation products were absent. Lymph von Willebrand factor antigen was < 10% of plasma antigen and consisted primarily of lower molecular weight multimers. Mean lymph-to-plasma activity ratio for antithrombin was 0.38 and for tissue factor pathway inhibitor the ratio was 0.40. Low levels of antithrombin-factor Xa were measurable in lymph. The data are compatible with a basal factor VIIa-tissue factor-catalyzed extravascular activation of factor X that is prevented from progressing to generation of fibrin in limb interstitial fluid and lymph by low levels of factor VIII and factor V and by the inhibitory activity of antithrombin and tissue factor pathway inhibitor.